1. Field of the Invention
This invention relates to a method for deodorizing tall oil, to include tall oil fatty acids, tall oil rosin, tan oil fatty acid derivatives, and tall oil rosin derivatives. More particularly, this invention relates to a method for deodorizing esterified tall oil fatty acids and tall oil resin acids. Most particularly, this invention relates to a method for deodorizing tall oil fatty acid and rosin esters with subsequent enhancement and preservation of the odor improvements with certain antioxidants.
2. Description of the Prior Art
Tall oil is derived from a soapy material consisting of the sodium salts of rosin and fatty acids produced, in addition to the desired paper pulp, by the sulfate pulping process. In the primary sulfate pulping process, the kraft process, the fatty acid glycerides are saponified and, along with the free resin acid glycerides also existing in the living pine tree, are converted to sodium soaps. These soap "skimmings," recovered from the kraft black liquor, are convened to crude tall oil (CTO) by reaction with sulfuric acid. The CTO is upgraded by an initial distillation and then is separated into tall oil heads, distilled tall oil, tall oil rosin, and tall oil fatty acids (and/or various fractions of rosin and fatty acids) by subsequent distillations. Throughout the various treatments to which the crude tall oil is subjected, the residual sulfur contaminants from the sulfate pulping process persist in its various products. Often this results in color and odor problems which may limit product applications. This invention method is directed to all of these products of CTO and their derivatives. More particularly, the invention method is directed to esters thereof. Most particularly, the invention method is directed to the pentaerythritol esters of distilled CTO, tall oil heads, rosin, and tall oil fatty acids-primarily to rosin and fatty acid pentaerythritol esters.
Rosin, as a solid resinous material that occurs naturally in the oleoresin of pine trees, may be extracted by means other than tall oil distillation. The three major sources of rosin are: from the oleoresin extrudate of the living pine tree (gum rosin); from the oleoresin contained in the aged stump of the longleaf pine (wood rosin); and from the tall oil produced as a by-product in the kraft paper industry (tall oil rosin). The rosins to which this invention relates include tall oil rosin and derivatives thereof.
Rosin is a complex mixture of mainly C.sub.20 -fused ring, mono-carboxylic acids, typified by levopimaric and abietic acids, and a small amount of nonacidic components. Its color, depending on the source and method of processing, can vary from a very pale yellow through dark red to almost black with a tinge of red. It is generally translucent, brittle at room temperature, and has a slight turpentine odor and taste. It is readily soluble in most organic solvents, such as ethyl alcohol, ethyl ether, mineral spirits, and benzene; it is insoluble in water.
As obtained from its three major sources, rosin is described as "unmodified." The resin acid molecule possesses two chemically reactive centers, the double bonds and the carboxyl group. Reactions at the double bond include isomerization, Diels-Alder and Ene addition reactions, oxidation, hydrogenation, dehydrogenation, and polymerization. Reactions at the carboxyl group include salt formation, esterification, hydrogenolysis, ammonolysis, and decarboxylation. Such reactions, however, are employed to increase the stability and improve the physical properties of rosin, producing "modified rosins."
As stated earlier, the chemical modification of tall oil to which this invention particularly relates is esterification, although it may include esterified fatty and resin acids which also are modified at the double bond. The beneficial product characteristics provided by tall oil fatty acid and rosin esterification for various applications have led to the development of many esterification procedures, particularly treatments with polyhydric alcohols. U.S. Pat. Nos. 2,369,125, 2,590,910, and 2,572,086 (the disclosures of which are incorporated herein by reference) teach rosin esterification with glycerol and pentaerythritol, among other polyhydric alcohols, usually preceded by a rosin disproportionation step.
Rosin ester tackdriers for adhesive products have been used for many years. Traditionally, the tall oil resins have been considered far inferior in odor characteristics to both gum rosin and wood rosin resins. This has been attributed to their high sulfur content due to the chemicals employed in the kraft pulping processes that produce the tall oil-containing black liquor and the elevated temperature history that the tall oil rosin experiences during fractionation of the crude tall oil into fatty and resin acids. Instead of the pleasant "piney" odor of wood or gum rosin, the tall oil rosin exhibits a strongly pungent, burnt quality of odor. As this odor can be carried over into the derivative product and can be intensified by the derivation processing (i.e., esterification at high temperatures), it has limited the use of tall oil rosin derived tackdriers in a number of adhesive areas. Many attempts have been made to improve the odor of tall oil rosin ester tackdriers. Thus, the greatest benefits of this invention are derived when applied to tall oil rosin esters.
Though not specific to tall oil rosin, U.S. Pat. No. 4,970, in 1847, disclosed a method of bleaching rosin by means of alkali, artificial heat, and water, without reporting any effect on odor. U.S. Pat. No. 1,694,179 describes the injection of superheated steam in the vacuum distillation of wood rosin to remove volatile color bodies. Modern tall oil rosin products already having taken advantage of these types of processes are still deficient in odor characteristics.
Likewise, tall oil fatty acid esters produced by traditional esterification techniques possess the latent sulfur or mercaptan odor of the original feedstock, whether it is tall oil heads, distilled tall oil, or tall oil fatty acids. Esterification of tall oil fatty acids is well documented and, with the exception of reaction with methanol, generally can be conducted at atmospheric conditions in an agitated vessel equipped with heating coils and an upright retire condenser. A nitrogen blanket and/or sparging typically is used to protect the product from oxidation, resulting in a product of light color. The product odor, however, can limit application and uses.
For example, the pentaerythritol ester of tall oil fatty acids is known to function as a synthetic lubricant and coolant in the metalworking industry where extreme heat is created due to the friction at the point of contact of the machine tool and the work piece. When the tall oil fatty acid ester is sprayed onto the work piece to alleviate the friction and to reduce the high temperatures, the heat volatilizes the low molecular weight constituents in the metalworking fluid. In addition to agomization of the fluid in the immediate work area due to the high velocity at which the work piece is turned, the volatilization results in furthering the objectionable odor experienced by the workman, whose complaints have limited such use of tall oil fatty acid esters in this application.
Also, unrelated to tall oil rosin, U.S. Pat. No. 4,915,876 discloses a deodorization process for fish oils involving use of mild solutions of acids and/or bases in sequential distillations "to realize highly polyunsaturated oils of enhanced stability."
Purification of wood and gum rosin derived resin is taught by U.S. Pat. No. 2,369,409 to involve mixing with fatty acids, saponifying of the mixture, subjecting the saponified mixture to a strong current of steam or other inert gas, and recoverying (by separating) the resin. This process is complicated and, due to the enhanced odor problems with tall oil rosin, would require multiple treatments, proving uneconomical.
As it is generally known in the art that a significant disadvantage of pentaerythritol esterification of tall oil rosin (as compared with glyerol esterification) is the deterioration of rosin color in the product of the former process, many methods have been developed to improve tall oil rosin pentaerythritol ester color. Some methods teach pre-esterification rosin treatments, such as U.S. Pat. Nos. 3,780,012 and 4,962,186. Other methods teach specific esterification catalysts or catalyst combinations, such as U.S. Pat. Nos. 2,729,660, 3,423,389, 3,780,013, 4,172,070, 4,548,746, 4,725,384, and 4,585,584. None of these teachings, however, suggest rosin ester odor improvements.
The object of the present invention, therefore, is to provide an effective, economical method for deodorizing tall oil rosin and fatty acid ester products and, simultaneously, maintaining or improving product color.